1. Field of the Invention
The present invention is in the field of machines used to inspect the alignment and location of various articles and generally relates to those machines known as optical coordinate measuring machines. More particularly it pertains to a precision video gauging machine machine for measuring relatively small or relatively lightweight workpieces that are mounted for movement in a vertical relationship to a base element plane to a base element while an optical measuring system is being operated in a horizontal relationship to the base element for benefits and reasons being explained and expanded upon below.
2. Description of the Prior Art
Coordinate measuring machines are well known in the art. Two main types of such coordinate measuring machines are the probe type and the optical type.
The probe type coordinate measuring machine typically has a probe mounted on a probe shaft, which is movable along a first axis to make measurements of a part. The probe shaft is typically mounted to a carriage which is movable along a second axis orthogonal to the first axis. The second axis is typically mounted to a carriage which is movable along a second axis orthogonal to the first axis. The second axis is typically movable along a third orthogonal axis, thus allowing the probe to take measurements in all three coordinate axes. The movement of the probe or carriage is accomplished either manually in one type of machine, where an operator grasps the probe shaft and physically moves it in the desired direction, or automatically in a more sophisticated type of machine where it is moved by an automatic controller driving a motor on each axis.
The optical type of coordinate measuring machine typically provides for relative motion (along three Cartesian coordinate axes) between a workpiece to be measured and a video camera, a laser ranging device, or laser triangulation device used similar to the mechanical touch probe described above. A well known type of optical coordinate measure machine is the projection type where a workpiece is placed on a horizontal table that is illuminated from underneath and the outlines of the workpiece are projected onto a screen for an operator. The operator moves a device, usually a camera, over the illuminated workpiece marking points of interest and an associated mechanical or computer system keeps track of the movement of the device for telling the operator the coordinates selected and their relative position to a known or selected datum.
Recently some coordinate measuring machines have attempted to combine both the touch probe and video imaging mechanisms by including touch probes and laser imaging devices. However, these hybrid machines are typically just two inspection devices mounted side by side.
By way of example, the prior art includes U.S. Pat. No. 4,305,207 to Lantz discloses a three axis inspection machine; U.S. Pat. No. 4,503,614 to Tuss provides a coordinate measuring machine having vertical fine fee and lock mechanism for its probe shaft; U.S. Pat. No. 4,651,426 to Band et al. provides a portal type coordinate measuring machine; U.S. Pat. No. 5,825,666 to Freifeld provides an optical coordinate measuring machine using an optical touch probe; U.S. Pat. No. 6,058,618 to Hemmelgarn et al. teaches a coordinate measuring machine with a gantry structure.
Each of these types of coordinate measuring machines has its benefits and drawbacks in practical use over the wide range of workpieces that a common in industry. For example, these coordinate machines typically lay the workpiece to be measured on a horizontally movable table and utilize a gantry type structure for moving the coordinate measuring probe or camera vertically over the workpiece. Thus, it is obvious that the table on which the workpiece is laid must be sufficient to support the weight of the workpiece. However, this is a factor in limiting the type of workpieces that me measured because such tables must also allow for illumination of the workpiece from the bottom. Typically such inspection tables have their central portion made of glass or a translucent plastic material to allow such bottom illumination of the workpiece. Warnings are common that workpieces above certain specified weight limits would damage the inspection table as the central portion cannot support such heavy items. Likewise, many workpieces when laid on the inspection tables have pressure or stress points that exert or concentrate the weight of the workpiece into a small area, causing damage to the surface of the inspection table and the uniformity of the illumination source, thereby potentially causing inaccuracies in the measuring system of the machine. In summary then, the need to illuminate the workpieces from underneath on such inspection tables limits the weight that can be placed on such inspection tables and hence the range of workpieces that can be measured.
Secondly, the gantry type structures used to hold and move the measuring probe, be it mechanical, touch or optical, limits the vertical size of workpiece that can be measured with the machine. Large or deep workpiece configurations simply cannot fit under the gantry structure and therefore cannot be measured by the machine.
Third, especially in the projection type of coordinate measuring machines mentioned above, changing lenses on the camera to accommodate various sized workpieces with the optical projection system, is both inefficient, as it is time consuming, and costly, as many expensive lenses must be purchased and maintained.
Therefore, it can be appreciated that in modem manufacturing where quality control is becoming of paramount importance in mass manufacturing of items on a worldwide basis from many different countries and plants, there exists a continuing need for a new and improved coordinate measuring machine for providing accurate measurements for quality control information that is both easy to use, adaptable to the wide range of potential workpieces, durable, and that overcomes the limitations of the prior art as to the deficiencies noted above as well as to other aspects of the prior art as is better described below.